Passenger conveyors such as escalators and moving walkways are provided with emergency braking systems which will stop movement of the conveyor steps or treads and of the handrail in the event of an emergency condition. An emergency condition can include intrusion of a foreign object in the handrail reentry housing; intrusion of a foreign object between a step or tread and the exit landing comb plate; failure of a component of the conveyor; or the like.
When an emergency condition occurs, the conveyor microprocessor controller is preprogrammed to stop further movement of the conveyor, and also to complete the stopping of the conveyor within a predetermined time period which will provide a comfortable cessation of conveyor movement for the passengers on the conveyor, while at the same time minimize the duration of the emergency condition. The time needed to stop movement of the conveyor is inversely proportional to the braking force applied to the drive sprocket axle, thus, all things being equal, the escalator will stop quicker if a greater braking force is applied. The problem encountered with emergency braking is that one cannot predict how much braking force will have to be applied to the conveyor to stop within the predetermined time period because one cannot know how many passengers will be on the conveyor when an emergency situation arises. Thus, one must set the braking force at some passenger load value. This can result in an unduly abrupt cessation of conveyor movement when the conveyor is lightly loaded. Thus, it would be desirable to have a system which will periodically adjust the emergency braking force to be applied to the drive sprocket axle to reflect the currently existing passenger load on the conveyor.